The present invention relates to a novel organic extraction and/or solubilisation solvent comprising at least one compound selected from the group of saturated monocyclic terpenoids, to an extraction method using said solvent, and to extracts obtained by said method.
More particularly, the invention relates to a novel use of para-menthane, a saturated monocyclic terpenoid compound, as a solvent derived from natural substances, and is also directed to a solvent comprising para-menthane.
A further object of the invention is to define an extraction and solubilisation method using said solvent, especially in liquid/liquid or solid/liquid extraction methods, as well as extracts obtained by carrying out this method.
The solvent according to the invention can be used for the extraction and/or solubilisation of plant and/or animal and/or prokaryotic biological material.
Preferably, said solvent will be used for the extraction and solubilisation of active natural compounds from a plant extract or from plant matter of natural origin.
Active natural compounds are molecules obtained from a plant material which have an activity of biological and technological interest. These active natural compounds can be in pure form or contained in extracts. Active natural compounds belong to the category of pigments, including carotenoids and chlorophylls, flavourings, including terpenes, and plant oils, including triglycerides or phospholipids. These active compounds can be used in food, cosmetic, pharmaceutical and nutraceutical applications.
The expression “natural compounds” refers to various categories of biochemical compounds. Apart from plant fats, small amounts of these compounds are usually present in plant matrices. A distinction is thus made between several categories of natural compounds according to their chemical nature:                Pigments: can be present in the form of partially hydroxylated carbon chains containing an aromatic ring. Lipophilic pigments can be obtained by concentration of extracts obtained from plants called oleoresins. Pigments are distinguished according to their colour, for example: carotenoids (yellow, orange or red colour), anthocyanins (red to violet or even blue colour), xanthophylls and curcuminoids (yellow colour), chlorophylls (green colour) and phycocyanin (blue colour).        Flavourings: this category of compounds refers to volatile compounds which are present in essential oils, concretes and absolutes of flowers, for example. Molecules of the terpene type (their chemical structure is composed of an aromatic ring containing hydroxyl groups) constitute a large proportion of the flavourings. The aromatic profiles of plants are dominated by a number of terpenes, depending on the plants. For example, basil essential oil is composed mainly of linalool, estragole, eugenol and methyl eugenol.        Plant oils: these mixtures contain compounds of which the main chemical structure is a carbon chain typically having 14 to 20 carbon atoms (the units forming the fats are called fatty acids) and an unsaponifiable fraction (polar lipids, sterols, etc.). Plant oils are lipophilic compounds and extracts containing fats are in the form of oil or solid fatty plant material containing triglycerides or phospholipids.        
The procedure that is most widely used for obtaining natural compounds is solid/liquid extraction. There are a number of conventional methods of solid/liquid extraction, such as maceration, percolation, lixiviation and decoction. Traditionally, these methods use water and ethanol to obtain natural extracts. However, these solvents permit the solubilisation mainly of hydrophilic compounds with low selectivity.
Other solvents are used for a more selective extraction. The solvents that are most widely used in the extraction of natural substances are organic solvents such as hexane, methanol, dichloromethane and acetone. These solvents are very effective substances which dissolve solid and liquid solutes, and their volatility facilitates their removal at the end of the method. However, a large number of organic solvents are also flammable, very volatile and toxic (carcinogenic, mutagenic, etc.). A number of works have already been carried out on their harmful effects (Baldasseroni et al., 2003; Manini et al., 2004). In addition, the gradual depletion of oil resources and increasing regulatory constraints are encouraging a trend towards alternative solvents. Thus, many studies aim more particularly to replace hexane with other solvents which would allow an equivalent extraction yield to be obtained and which would be less harmful.
Hexane is a molecule which is classified in the category of “carcinogenic, mutagenic and reprotoxic” (CMR) molecules of class 3 (EU CMR list), that is to say as a reprotoxic molecule. The physico-chemical characteristics of hexane make it dangerous to handle. Hexane has a low flash point (23.3° C.) and an auto-ignition temperature of 233.9° C.
Various solvents have been proposed to replace hexane.
Plant oils can be used as an extraction solvent for non-volatile compounds. The enrichment of the oils is then limited by the solubility of the plant extracts in the oil, permitting only partial extraction of the natural compounds contained in the treated plants. Agro-solvents of the methyl-THF type have been used for extraction (Sicaire et al., 2014), but the main industrial constraint is based on the reactivity of 2-methyl-THF with plastics materials.
Other agro-solvents of the terpene type obtained from co-products of the agri-food industry have been proposed for the extraction of natural compounds. Terpene solvents such as limonene or alpha-pinene (for example WO 2007/057549 A2) can have chemical reactivity due to the presence of double bonds. Thomas and Bessière (1989) show the existence of numerous conversions of limonene following chemical reactions, for example of the acid-base, epoxidation, hydrogenation and oxidation type. Limonene therefore constitutes a species which is reactive in solution. The conversions of limonene involve a modification of its structure by rearrangement and reaction of the double bonds with other chemical species present in solution.
It is known from Karlberg et al. (1992) that limonene, when exposed to air, undergoes auto-oxidation reactions which lead to the formation of oxygenated derivatives of the hydroperoxide type. The compounds formed are, moreover, allergenic. In addition, the auto-oxidation reaction of terpenoids (such as limonene, thymol, citral and alpha-pinene, for example) leads to the production of free radicals (Turek and Stintzing, 2013), which can react with the target extraction compounds, resulting in the degradation thereof.
In order to remedy the disadvantages of terpene compounds containing double bonds, it is possible to consider a terpene analogue that does not contain double bonds. Several teams of chemists mention obtaining a molecule called para-menthane (1-isopropyl-4-methylcyclohexane, FIG. 1) by catalytic hydrogenation (US 2013/0281747 A1 of Chink et al., 2013, Li et al., 2014, Shuikin and Cherkashin, 1957).
Para-menthane has been mentioned in various patents.
Para-menthane has been mentioned for chemical applications, especially as a compound formed during reactions or as a reagent. Accordingly, U.S. Pat. No. 2,400,012 A describes a process for obtaining para-cymene by catalytic dehydrogenation. This reaction leads to the formation of a mixture composed of para-cymene and para-menthane. In this invention, the para-menthane formed is reused for the purpose of recycling in the dehydrogenation reaction. Para-menthane is used in another invention (U.S. Pat. Nos. 2,302,463 and 2,302,468) in a liquid-phase reaction with oxygen. There is described therein a reaction aimed at converting para-menthane in order to obtain alcohols, aldehydes, ketones and acids. A process for sulfurisation of terpenes is described in U.S. Pat. No. 2,537,297. The sulfurisation is carried out on mixtures of terpenes, which can include para-menthane. U.S. Pat. No. 2,597,372 describes obtaining cyclopentane hydrocarbons and benzenoid hydrocarbons by reacting para-menthane and isocamphane in the presence of a palladium-type catalyst. Accordingly, since these inventions refer to the presence of para-menthane in chemical conversion reactions, they do not relate to the solvation properties of para-menthane with respect to natural compounds of interest.
Para-menthane has been proposed as a component of a mixture for removing inks (JP2005023196). The use of cleaning mixtures containing, inter alia, para-menthane has been described by the company Refining Oils in several patents (US20040102351, US20040238006 and U.S. Pat. No. 6,872,263). The inventors found a formulation of a cleaning agent comprising a saturated monocyclic terpene compound and a non-ionic surfactant. This mixture is used by being injected into a vapour phase circulating in the pipes and containers to be cleaned. In a later patent of Refining Oils (US20110056694) there is described a method for removing paraffins and bitumens in oil refining processes. The cleaning agent described is composed of para-menthane with or without an additive of the surfactant type. The spectrum of action of this agent is aimed at non-natural apolar compounds of very high molecular weight and additionally functions in a process using this mixture in the vapour state. A terpene-based formulation similar to the patents cited hereinbefore is referred to in EP 0781842 A2. This latter patent describes a non-liquid cleaning mixture composed of from 90% to 96.5% of a halogenated compound (n-propyl bromide), from 0 to 6.5% terpene compounds and from 3.5 to 5% compounds having a low boiling point. This chemical cleaning agent is used in the vapour phase at temperatures of about 70° C. to dissolve mineral oils, silicone oils or metals. In all these inventions, which are aimed at describing cleaning processes, there is no mention of the use of para-menthane for the extraction and solubilisation of natural compounds obtained from natural plant materials.
Accordingly, para-menthane has been mentioned for chemical applications or as a component of mixtures in cleaning processes. There is a continued need to identify alternative solvents to replace hexane that allow targeted natural compounds to be extracted or specifically solubilised, while obtaining at least identical yields.